The state was a must-win for Kasich, who is openly vying to win the nomination in a contested convention, and said he would drop out if he did not win his home state.

Kasich's victory also makes Trump's path to securing the 1,237 delegates needed to claim the nomination somewhat more difficult.

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John Kasich on the campaign trail

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John Kasich is projected to win Ohio

MILFORD, NH - SEPTEMBER 7: Republican presidential candidate John Kasich greets supporters at the Labor Day parade on September 7, 2015 in Milford, New Hampshire. Kasich, buoyed by what observers called a strong performance in the first GOP debate, has emerged as a first tier presidential candidate with voters in New Hampshire, the nation's first primary state. (Photo by Kayana Szymczak/Getty Images)

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In the days leading up the primary, polls showed Kasich running neck and neck with Trump in the Buckeye State. Trump campaigned hard in the state in the final days, canceling a Florida campaign event Monday night and scheduling a rally in Ohio in its place.